1. Field of the Invention
The present invention relates to an injector for fuel injection.
2. Description of Related Art
An injector for fuel injection attached to an intake pipe of an internal combustion engine is known. For improving engine performance and for purifying exhaust gas, the injector is required to atomize fuel which is injected.
JP-A-08-277763 and JP-A-09-310651 disclose nozzle hole plates (also called orifice plates) formed with fine nozzle holes (also called orifices). According to these conventional techniques, fuel is injected from the orifices and is atomized. In each of these constructions, consideration is given to the flow of fuel upstream with respect to the orifice plate which contributes to the atomization of fuel. However, due consideration is not given to the path which the fuel should follow after injection. For example, in the case where the flow velocity of engine intake air is high, the spread of spray is partially obstructed and there is a fear that a portion of fuel may adhere to a tip portion of the injector and stay there as a drop. Further, Upstream the orifice plate there is formed a dead space between the plate and a valve member, so that the fuel staying in the dead space may leak out to the underside of the orifice plate and form a drop under the action of an intake negative pressure.
The adhered fuel gives rise to an undesirable difference between a target fuel quantity preset by a controller and an actual fuel quantity fed actually to a combustion chamber. Such a difference causes a deficient engine output, a lowering of response characteristic, and an increase of undesirable exhaust gas components.
It is an object of the present invention to provide an injector which can decrease the amount of fuel adhered to a tip portion of the injector.
It is another object of the present invention to provide an injector wherein the amount of adhered fuel does not increase even if the fuel is atomized to a high degree.
It is a further object of the present invention to provide an injector which can recover fuel adhered to its tip portion and can inject the recovered fuel.
According to a first feature of the present invention, the injector has an orifice plate formed with orifices. A highly atomized fuel is injected from the orifices. A portion of the fuel adheres to a tip portion of the injector. Downstream the injector orifice plate is formed a negative pressure region as the fuel is injected from the orifices. This region is designated a negative pressure forming section. The injector is provided with a recovery section. The recovery section conducts the adhered fuel toward outlets of the orifices by utilizing a negative pressure developed in the negative pressure forming section. By the recovery section there occurs a flow of adhered fuel toward the orifices"" outlets. The adhered fuel flows through the recovery section and is returned to a main jet formed from the orifices. As a result, an increase in the amount of fuel adhered to the injector tip is suppressed. There may be adopted a construction wherein plural orifices are formed in an orifice plate so as to be inclined divergently from a valve step of the injector. Such a divergent inclination permits utilizing a negative pressure developed at the injector tip. Plural orifices may be arranged so as to cross the orifice plate in the diametrical direction. For example, the orifices may be arranged in plural rows or in plural rings.
When fuel is injected from the orifices, a negative pressure is developed on the orifice plate, which is based on direction of fuel injection. This negative pressure is conducted radially outwards along the upper surface of the orifice plate. Consequently, there is formed an air stream flowing inwards from a radially outside of the orifice plate. The adhered fuel flows along this air stream.
The recovery section may be provided with a wall surface extending from the underside of the orifice plate downstream. The wall surface is disposed outside and near a circumscribed circle of outlet-side openings of the plural orifices. Fuel adhered to the wall surface is conducted toward the orifices"" outlets under the action of a negative pressure developed in the negative pressure forming section. The wall surface may be circular or elliptic, or it may be formed by plural walls. The wall surface stabilizes the generation of a negative pressure in the negative pressure forming section and provides a path for the flow of adhered fuel.
The recovery section may be provided with a passage for radially conducting the negative pressure developed in the negative pressure forming section. Through this passage the adhered fuel flows toward the negative pressure forming section and thus the recovery of the adhered fuel is promoted.
According to another feature of the present invention, the injector has an orifice plate provided at a tip thereof and formed with orifices for the injection of fuel and also has a catch member for catching fuel adhered to the tip of the injector. The catch member forms a path for allowing the adhered fuel to flow toward an upper surface of the orifice plate. Consequently, the adhered fuel is returned to the orifice plate and is injected again.